Respiratory apparatus with improved flow-flattening detection

Abstract

In a respiratory apparatus for treatment of sleep apnea and other disorders associated with an obstruction of a patient's airway and which uses an airflow signal, an obstruction index is generated which detects the flattening of the inspiratory portion of the airflow. The obstruction index is used to differentiate normal and obstructed breathing. The obstruction index is based upon different weighting factors applied to sections of the airflow signal thereby improving sensitivity to various types of respiration obstructions.

1. An apparatus for monitoring sleep apnea in a patient comprising:
 a flow sensor adapted to sense the flow of air breathed by the patient and to generate a flow signal indicative of said gas flow; and 
 an obstruction detector coupled to said flow sensor, said obstruction detector including a weight assigning member arranged to assign several weighting factors to portions of said flow signal and to generate an obstruction signal. 
 
   
   
     2. The apparatus of  claim 1  wherein said flow signal includes a section corresponding to a single breathing cycle and wherein said portions are selected from said section. 
   
   
     3. The apparatus of  claim 1  wherein said flow sensor includes a sampler that generates flow samples and wherein said weight assigning member is adapted to assign a weighting factor for each sample. 
   
   
     4. The apparatus of  claim 3  wherein said samples have amplitudes and said weight assigning member assigns said weighting factors to said samples in accordance with said amplitudes. 
   
   
     5. The apparatus of  claim 3  wherein said samples have time positions and said weight assigning member assigns said weighting factors based on said time positions. 
   
   
     6. An apparatus for monitoring a patient having sleep disorder, said apparatus comprising:
 a flow sensor to generate a flow signal indicative of the patient's respiration; and 
 an obstruction detector coupled to said flow sensor and adapted to determine a weighted average signal, said weighted average signal being dependent on a weighted average of said flow signal in accordance with an amplitude of portions of said flow signal. 
 
   
   
     7. The apparatus of  claim 6  wherein said obstruction detector includes a comparator adapted to compare said weighted average signal to a threshold, said comparator generating said obstruction signal. 
   
   
     8. The apparatus of  claim 6  wherein each portion has an amplitude and wherein said weight assigning member assigns said weighting factor based on said amplitude. 
   
   
     9. The apparatus of  claim 8  wherein said weight assigning member assigns said weighting factor based on whether said amplitude is above or below a predetermined value. 
   
   
     10. The apparatus of  claim 9  wherein said weight assigning member assigns a first weighting factor to portions having amplitudes lower than said predetermined value and second weighting factors to having amplitudes higher than said predetermined level. 
   
   
     11. The apparatus of  claim 10  wherein said first weighting factor is smaller than said second weighting factor. 
   
   
     12. The apparatus of  claim 6  wherein said flow signal includes a section corresponding to a single breathing cycle, and wherein said apparatus further includes a sampler sampling a portion of said section. 
   
   
     13. The apparatus of  claim 12  wherein said section corresponds to an inspiration period. 
   
   
     14. The apparatus of  claim 13  wherein said sampler samples a midportion of said inspiration period. 
   
   
     15. A method of monitoring a person with sleep apnea comprising the steps of:
 determining an air flow signal indicative of the air flow of the patient; 
 sampling a section of said air flow during successive breathing cycles to obtain a set of samples for a breathing cycle; 
 assigning a weight to each sample; and 
 generating an obstruction signal based on said weights and said samples from said set of samples. 
 
   
   
     16. The method of  claim 15  wherein said set of samples comprises samples from a midportion of inspiration. 
   
   
     17. The method of  claim 16  further comprising the step of generating an average of said midportion samples. 
   
   
     18. The method of  claim 17 , wherein each sample has an amplitude, further comprising the step of selecting a first weighting factor for samples having an amplitude below a predetermined threshold value and a second weighting factor for samples having an amplitude above said predetermined threshold value. 
   
   
     19. The method of  claim 18  wherein said first weighting factor is smaller than said second weighting factor. 
   
   
     20. The method of  claim 18  wherein said predetermined threshold value is a mean of said flow signal. 
   
   
     21. The method of  claim 17 , wherein each sample has a time position, further comprising the step of selecting a first weighting factor for samples having time positions prior to a predetermined time position and selecting a second weighting factor for samples having time positions after said predetermined time position. 
   
   
     22. The method of  claim 21  wherein said first weighting factor is smaller than said second weighting factor. 
   
   
     23. The method of  claim 21  wherein said predetermined time position is a central point of said midportion. 
   
   
     24. The method of  claim 16  wherein said obstruction signal represents the sum of the weighted absolute difference of the said samples from a midportion of inspiration divided by the product of a mean of the set of samples and the duration of said midportion.